This invention relates to a semiconductor element which is adapted for detecting radiation or light of a comparatively low energy level at a high sensitivity.
One radiation detecting semiconductor element according to the prior art consists of a surface-barrier type wherein a metal adapted to form a Schottky barrier is deposited on a semiconductor substrate. The metal adapted to form Schottky barrier may be gold for an n-type substrate, but may be aluminum for a p-type substrate. However, the mechanical strength of gold is comparatively low and thus tends to be easily stripped off the surface of the substrate, whereas aluminum exhibits comparatively low resistivity to ambient conditions and chemical corrosion. Particularly the radiation energy entering the depletion layer 5 through the silicon oxide layer 6 is maintained substantially at its original value, the radiation energy entering the depletion layer 5 through the electrode 3 and the diffusion layer 2 is partly reduced before entering the depletion layer. For this reason the measured radiation energy following the latter path is lower than the actual radiation energy.
FIG. 3 shows the measured results, with the abscissa representing the height of the pulse current delivered from the semiconductor element corresponding to the energy of each radiation, and with the ordinate representing the number of current pulses corresponding to the number of the radiation. A curve A in FIG. 3 indicates a case wherein .alpha. rays emitted from an isotope .sup.241 Am are measured by a planar element shown in FIG. 2. The peak values appearing on the right side in FIG. 3 correspond to energy levels inherent to the .alpha. rays, while the peak values on the left side of FIG. 3 correspond to the energy levels reduced by the electrode 3 and the diffusion layer 2. In the conventional planar type radiation detecting semiconductor element, an abnormal spectrum appears beside of the normal spectrum, and the number of the radiations corresponding to the abnormal spectrum frequently exceeds the number of radiations corresponding to the normal spectrum as shown in FIG. 3.